The present invention relates to an improvement in a covering device employed by truck trailers with an open top configuration used for the transportation of loose materials. More specifically, to a device which makes the covering of the open box of a belly dump type trailer with a tarpaulin much more effective and with less chance of down time due to damage or breakdown.
A belly dump trailer is a type of open top trailer that is most commonly used to transport construction materials such as sand and gravel. The name "belly dump" comes from the manner in which the material that is being transported is emptied from the box of the vehicle. The belly dump trailer's open box extends downward below the lowest surface of the trailer frame and this extension is open to the surface beneath the trailer. This opening is closed off by the use of a pair of pivotally mounted clam-type doors that can be hydraulically opened and closed by the operator of the vehicle. Thus, when the load being carried by the trailer is to be dumped, the doors are opened and the material contained in the trailer's box is dropped to the ground below.
The problem with this style of load carrying trailer is that it is most commonly used to transport loose materials and federal, state, or local law often requires that such loads are covered during transport. This, in and of itself, does not pose a significant problem as there are many available styles of tarpaulin covers specifically designed for use with all types of trailers. The problem with covering loads carried within belly dump trailers stems instead from the use of electric drive motors commonly employed to roll and unroll the tarpaulin over the load.
The method commonly employed to roll and unroll the tarpaulin is to install an electric drive motor on the front portion of the belly dump trailer. This electric motor is connected to the roll tube (the device used to direct and store the tarpaulin in the rolling and unrolling process) by the use of drive shaft that contained a universal joint at either end. The purpose of these universal joints is to compensate for both the varying angles created between the drive motor and roll tube as the roll tube passes over the load box and the differences in the longitudinal axis of the drive motor and the roll tube. This problem is a result of the respective locations of these two components as the drive motor is most commonly mounted on the trailer frame well below the roll tube.
This design works well in compensating for these specific variables but there is another variable relationship created in this application. The final variable is a result of the fact that the distance between the electric drive motor and the leading edge of the roll tube is shorter when the roll tube is located at the center of the box than it is when the roll tube is located at either side of the box. In the past, this problem was dealt with by the use of a telescoping drive shaft that either expanded or contracted depending on the position of the roll tube. The problem with this design is that, by its very nature, the telescoping drive shaft created a weak point in the drive mechanism that was often the source of operation down time due to its failure.
From the foregoing discussion, it can be seen that it would be desirable to provide a method that eliminates the use of telescoping drive shafts commonly employed to roll and unroll tarpaulins that are used to cover loads carried in belly dump trailers. The replacement of the telescoping drive shaft would improve the efficiency of these load covering systems by decreasing the amount of down time encountered in replacing or repairing broken or damaged drive shafts that are used in this application today.